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Issue 11

Table of Contents

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Myofascial stiffness of plantar fascia and achilles tendon in individuals with plantar fasciopathy: An observational cross-sectional study

Dr. Cody Misuraca PT, DPT

Key takeaways:
  • Symptomatic limbs had decreased stiffness of the achilles tendon and plantar fascia compared to the contralateral, and asymptomatic limb respectively
  • There are some concerns regarding validity for current in vivo measures of tissue stiffness
  • There is still uncertainty as to what role tissue stiffness plays in symptomatic plantar fascia
  • Stretching can still be a useful entry point to loading and can open the door to more active loading plans like plyometrics and foot/ankle strengthening

 

One of the more interesting aspects of my position as a rehabilitation clinician that works under a hospital umbrella is listening to the explanations that have been provided to patients by other providers regarding the “what” and “why” of their painful conditions. The more providers a person has seen prior to coming to me for a given issue, the longer that list tends to be. For plantar fasciitis, however, the explanations given seem to be mostly centered around tightness – tightness of the calf muscles, tightness of the ankle joint, tightness of the plantar fascia itself.

Indeed, many people with plantar fasciitis will feel a sensation of stiffness around their foot and/or ankle, can present with limited range of motion, and tend to feel better when given stretches to work on. But if you’ve been following along with Across the Continuum for a while, I’m sure you recognize that pain is often more complex than that…

Enter Article #1 of this month’s research review¹, which compared foot/ankle tissue stiffness between people with and without plantar fasciitis. This was a cross-sectional study, and they used a novel application of a device called an “indentometer” to quantify tissue stiffness in the gastrocnemius, Achilles tendon, and plantar fascia. There have been a couple studies published previously on plantar fascia stiffness using shear-wave elastography, but the authors of this study wanted to use a measurement device that would be more applicable in a clinical setting.

An indentometer is essentially a pressure probe, measuring how much force is required to produce a given amount of deformity when pressed into a tissue. The stiffer the tissue, the more force it would take to push the probe a certain depth, and vice versa for less-stiff tissues. This study collected data from 39 people with a clinical diagnosis of unilateral plantar fasciitis, and 39 people without. The two groups consisted of a mix of men and women and had similar average ages hovering around the mid-40’s.

Ultimately they found that those with plantar fasciitis presented with decreased stiffness of the Achilles tendon compared to the corresponding limb of asymptomatic group members, and with decreased stiffness of the plantar fascia relative to their asymptomatic limb. This is generally in agreement with previous studies using shear wave elastography to assess plantar fascia stiffness in people diagnosed with plantar fasciitis. Before discussing the implications of the results of this and previous studies, I think it’s important to touch on the validity of measurement methods used to assess tissue stiffness.

In the case of this study, indentometry was performed in vivo in living humans – the measurement was performed clinically, meaning the indentometer was being pressed into the underlying tissue through the overlying skin; this does raise the question of how well this device is measuring stiffness of the underlying tissue and to what degree the overlying skin may confound the results.

One study has assessed the reliability of this particular device, finding good intra- and inter-rater reliability for in vivo measurements of stiffness at gastrocnemius sites², but did not assess reliability at Achilles or plantar fascia sites. The authors of the present study performed a pilot study on test-retest reliability of this device with the sites used for the primary study, demonstrating overall good reliability between sessions¹.

Another study using a different indentometer device to assess stiffness of the Achilles, plantar fascia, and gastrocnemius heads in varied positions of the lower limb found measurements that were in agreement with existing studies of tissue stiffness at similar sites using shear-wave elastography³. These studies would suggest that the indentometer used in this study was reliable for gastrocnemius sites, and valid when compared to elastography measurements of tissue stiffness at Achilles, plantar fascia, and gastrocnemius sites.

That said, a systematic review of measurement properties of shear wave elastography has raised questions regarding its reliability and validity⁴, which makes me hesitant regarding the certainty of the stiffness measurements in the present study. At the end of the day, I don’t think the results of this kind of study should significantly alter the trajectory of treatment for plantar fasciitis. I do believe that narratives given regarding why people have developed their symptoms are important, and I’m not a huge fan of telling people that their tissues are either too stiff or too lax without solid underlying evidence and good reason to think that their treatment plan should be significantly different because of it.

In the case of plantar fasciitis, if the stiffness of the plantar fascia and Achilles is truly decreased, we could hypothesize that this is an underlying trait that contributed to their symptoms, or an adaptive quality that presents secondary to long-term unloading of a painful area; we don’t have any way of knowing for certain which of these is the case based on cross-sectional data alone.

Stretching is still potentially beneficial in the setting of a tissue with reduced stiffness – for many people it is an effective short-term symptom modulator, and it can also serve as an entry-point for applying tension to the tissue as a stimulus for developing both increased load tolerance and potentially increased stiffness in the long-term. We of course also need to ask ourselves whether the observed degree of reduced tissue stiffness in this study is inhibitive of regaining baseline function of the foot/ankle, and whether it needs to increase in order for somebody to feel better and get back to doing what they want; those are questions for other studies that we just don’t have yet.

I personally like to instruct people with plantar fasciitis in various stretches as self-management tools for their pain, and also like to use foot/ankle strengthening and plyometric exercises for developing capacity to handle higher-threshold tasks. These interventions may or may not have a secondary benefit of increasing tissue stiffness, but if the person achieves an acceptable symptomatic and functional state as a result of working on these things, perhaps it doesn’t matter. We will have to keep our eyes peeled for future research to address these questions.

In the meantime – given the current available evidence – I wouldn’t be comfortable perpetuating the narrative that increased stiffness of the plantar fascia or calf musculature is an underlying cause of plantar fasciitis.

 

References:

 

Free-weight and machine-based training are equally effective on strength and hypertrophy: Challenging a traditional myth

Dr. Cody Misuraca PT, DPT

Key takeaways:
  • Both groups demonstrated similar increases in muscle cross sectional area for all of the tested sites
  • Both groups reported less overall limb discomfort after 8 weeks of either free weight or machine training, and to a similar degree.
  • Subjects saw improvements in strength with both modalities regardless of which one they focused on for 8 weeks
  • Greatest strength improvements were seen in the mode of exercise that they spent 8 weeks training for prior to post-intervention testing

 

Our second article for this month’s research review is going to shift gears to focus more on strength and hypertrophy outcomes related to varying resistance training modes. When I first started getting serious about lifting weights after graduating high school in 2008, the modern “functional fitness” movement was in full-swing, thanks to an increased interest in “core stability” in the 1990’s and the growing popularity of training systems such as Crossfit in the early 2000’s.

I was initially most interested in becoming bigger and more muscular, and bodybuilding-style training had strong appeal – through various internet forums and online articles I was taught that machine training was an OK adjunct, but that free weights were king. The hypothesis was that free weights would result in greater activity of “stabilizing muscles,” resulting in a variety of superior training outcomes. The study we’re reviewing next¹ decided to put this to the test with a head-to-head comparison of two training programs utilizing the same general movement patterns, with the primary difference between them being free weight variations vs machine variations for each corresponding exercise.

The study design was quite comprehensive. Both the free weight and machine groups performed 4 exercises (squat, bench press, prone row, seated shoulder press) – the free weight group performed these exercises using a standard 20kg barbell with loadable plates, while the machine group performed the same exercise with specific machines that closely mimicked the trajectory of the free weight exercises. Following a 2-week familiarization period using both exercise modes, the participants participated in 1-rep max (1RM) testing for all 8 exercises, were stratified by relative strength (1RM divided by bodyweight), and then randomly allocated into either the free weight or machine group.

Each of the two groups was made up of 19 male participants, with at least 2 years of resistance training experience, who then performed 8 weeks of 3-times-per week training with their assigned training modality. The two groups were matched for total training volume, and relative training intensity was monitored and matched using velocity trackers with a target of 20% velocity loss for each set. Training loads were matched to target intensity by performing an assessment of mean propulsive velocity (MPV, or the average velocity during the acceleration phase of the concentric) of the first two reps of each exercise during sessions 1, 6, 11, 15, and 20, and load was adjusted for these and subsequent sessions to match the target intensity zone.

Given that some mechanical features of a machine such as counterweights, multiple pulleys in-system, and friction can confound the actual resistance corresponding to the amount of weight listed or loaded onto a machine, velocity tracking was used to better match the resistance used in each group. Primary study outcomes included muscle cross sectional area (CSA) of the quadriceps femoris, pectoralis major, and rectus abdominis muscles; 1RM for each exercise as well as MPV of loads greater than and less than 60% 1RM; and upper and lower limb discomfort assessed via the WOMAC and DASH questionnaires.

Following the 8 weeks of training, both groups demonstrated significant and similar improvements in 1RM, and MPV for loads above and below 60% 1RM; each group’s improvements in these measures were improved for all 8 of the exercises, but were especially higher for the exercise mode that they had trained. Both groups demonstrated similar increases in muscle CSA for all of the tested sites, and both groups also demonstrated decreased upper and lower limb discomfort via the WOMAC and DASH questionnaires.

Depending on how long you’ve been active in the fitness space, you may have heard the phrase “strength is specific.” That is, “strength” is the ability to produce force within a specific context. For instance, in powerlifting, “strength” is defined by the maximal amount of weight that one can successfully lift in the squat, bench press, and deadlift for one repetition while abiding by the technical standards laid out in rule book for that federation; in rehab, we might define “strength” as the peak force that somebody could produce isometrically against some sort of strain gauge such a dynamometer; in the sport of American football, “strength” could be defined as how effectively one player can push against or resist the forces imposed by another player.

As you can see, “strength” is dependent on the context it’s being measured in, and development of “strength” through training is likely to be most specific to the mode that was used to develop it; this is related to the SAID Principle, or Specific Adaptation to Imposed Demands. Therefore, it should be unsurprising that the subjects in this study saw their greatest “strength” improvements in the mode of exercise that they spent 8 weeks training for prior to post-intervention testing. Interestingly, the free weight group did demonstrate greater average improvements in MPV for loads above and below 60% 1RM when tested on free weight exercises, while the machine group demonstrated greater average improvements in MPV for these loads when tested on the machine exercises, but with large variability to not reach statistical significance.

This may suggest superiority of free-weight training for improvements in MPV across a broader set of contexts when using the training approach in this study, but further study is needed for certainty there. The lack of overall difference in muscle CSA improvements between the two groups was also an interesting finding. Given the reduced need for stabilization with machine-based exercises, one might hypothesize that muscle CSA increases for directly-trained muscles such as the quadriceps or pectoralis would be greater in the machine group.

Conversely, given the increased demand for stabilization for free weight exercises, you might expect greater muscle CSA improvements for indirectly-trained trunk muscles such as the rectus abdominis in the free weight group. Based on these data, it seems like the increased stabilization demands of the free weight exercises used in this study were not great enough to be inhibitive of muscle CSA development for directly trained muscles, and also not great enough to develop more muscle CSA development for indirectly trained trunk musculature.

Whether this carries over to training programs with a greater variety or volume of free weight exercises, or over longer training periods, also needs to be studied further in future research. I find the outcomes related to upper and lower limb discomfort measured via the WOMAC and DASH questionnaires to be interesting. Both groups reported less overall limb discomfort after 8 weeks of either free weight or machine training, and to a similar degree. Many people who participate in resistance training anecdotally report generally feeling fewer aches and pains when they train regularly, and the data from this study suggest a measurable effect in that regard.

Additionally, there are conflicting anecdotal reports regarding the effect of free weight and machine training on aches and pains over the long term, and this study suggests that either modality could have a positive impact on discomfort at least in the short term; more study is needed to elucidate if a long term effect or difference between modalities exists for this. As an aside it may be that the specific movements, amount of training volume, or relative training intensities used in this study play a role in the observed effect for upper and lower limb discomfort, and again, further study is needed for certainty regarding that.

In summary, this study suggests fairly comparable improvements in strength with machine and free-weight tests when either machines or free weights are used exclusively in training, with a greater effect for the trained modality – for athletes whose sport directly involves a gym-based movement such as the squat or bench press, a free-weight variation that mimics the competition task is probably best used in training, while machines are likely viable for athletes whose sport does not directly involve a gym-based movement.

For developing muscle CSA it appears that machine and free-weights are equally effective in the short term, and both modes of training can be expected to have similar outcomes related to upper and lower limb discomfort in the short term. When strength development is a primary concern, my recommendation would be to consider whether the goal task is closely related to an easily-reproducible gym-based exercise, and let that inform your exercise selection to some extent. If muscle CSA development is the primary goal, trainee preference should play a larger role. In both cases, access, repeatability, enjoyment, and meaning should be taken into account when developing the plan.

 

References:

 

Cody Misuraca is a physical therapist and strength coach in Seattle, WA. He works as a sports physical therapist for a community hospital system and also owns Waypoint Strength and Performance LLC, which offers strength coaching services. The views and opinions expressed in this review are those of the writer and do not necessarily reflect the views or positions of any institutions he is associated with.